Not applicable.
Not Applicable.
The invention relates generally to surgical tools for spinal stabilization, and to methods pertaining thereto. More particularly, this invention relates to a cannulated bone screw system for transfacet and translaminar stabilization of the spine.
Thoracolumbar injury is a common pathology of the spine that is responsible for the generation of back or neck pain suffered by many patients. Injury to this area of the spine usually results from a degenerative disc disease, infection or tumor. Treatment of the injury often requires surgical intervention to restore the structural continuity of the spine. The most common surgery for treating such an injury is spinal fusion. Spinal fusion is the surgical joining of one vertebral body to another. This type of treatment often involves internal bracing and instrumentation to stabilize the spine to facilitate the efficient healing of the spine without deformity or instability, while minimizing any immobilization and post-operative care of the patient.
A method suggested by Magerl for treating a thoracic or lumbar pathology involves fixation of successive vertebrae using translaminar screws. Conventionally, these translaminar screws extend through the spinous process and then through the lamina at the facet joint into and through the pedicle of the successively inferior vertebrae. Another current approach utilizes standard fracture fixation techniques typically employed in orthopedic fracture applications. Such fixation techniques can include the use of lag screws to compress bone fragments together. A combination of bone plates and bone screws is also commonly implemented under current fracture fixation techniques. These bone screws and plates provide internal support as the fusion occurs.
With these conventional surgical procedures, screw length is determined by trial and error, probing into the surgical site, or by measurement forceps. Not only are these imprecise and inefficient ways to determine screw length, but result in excess trauma to the injury site and add to the time required to complete the surgery. Further, current systems and methods do not sufficiently enable a surgeon to identify the final screw trajectories to avoid screw collision. There is thus a need for a system and method that provides measurement of appropriate screw length in an easy and reliable manner. There is also a need for improved control over the trajectory of the screw during implantation. Finally, it is desirable to identify appropriate screw insertion sites to ensure that the final screw trajectories will not collide.
The present invention provides a system of instruments and a method for using these instruments for effective spinal stabilization using cannulated bone screws. In particular, the system and method provide accurate and efficient measurement of the appropriate screw length to be inserted in a patient undergoing spinal stabilization surgery. The system and method offers improved control over the trajectory of the screw during implantation. In addition, the system of the present invention minimizes both the need to use fluoroscopy in conjunction with the implantation process and the visibility problems that exist when installing conventional bone screws in certain patients, e.g., severely obese patients, by enabling accurate orientation or placement of the cannulated bone screws. Moreover, the present invention facilitates proper screw placement by allowing the identification of appropriate screw insertion sites to ensure that the final screw trajectories will not collide.
One method of using the instruments of the present invention involves an improved surgical technique for the placement of cannulated bone screws for use in orthopedic and spinal applications. Specifically, the present method is directed to a surgical technique for the placement of cannulated bone screws for translaminar facet, transfacet, and general orthopedic applications.
The present invention provides a cannulated screw system for effecting the posterior stabilization of the spine. The screw system also acts as an internal fixation device during the time interval required for arthrodesis. The screws can be placed either translaminar or directly through the facets for posterior spine fixation. The bone screws provide internal support as fusion and healing occur.
The system of the present invention includes a guide instrument, an obturator, and a series of cannulae which slide over the obturator and index with the fiducial markings on the obturator to indicate appropriate screw length. In one embodiment of the invention, there is provided an anatomic guide instrument for use with a cannulated guide pin obturator for placement of a guide wire. The anatomic guide references the desired location of the screw tip, and holds and aligns the guide pin obturator. When assembled to the anatomic guide instrument, the obturator references the desired location of the screw head. By placing a surgical cannula over the obturator, measurement marks indicate the length that spans the intended trajectory of the bone screw, which is identified by the distal prong of the guide instrument and the distal end of the obturator.
In addition, the guide instrument incorporates a middle prong which can either reference bony anatomy or provide a visual cue to determine screw trajectory. This orientation can be important for certain applications, e.g., spinal applications, because it establishes a safe trajectory to avoid injury to the surrounding anatomy and nervous tissues. In addition, the use of a guide wire minimizes the risk of damage or fracture of the facet by providing a stable guide for the bone screw with solid bony support.
In another aspect of the present invention, the guide instrument incorporates a multi-position ratchet mechanism which allows the instrument to be manipulated into several geometric configurations, thereby providing the surgeon with an instrument geometry suited to avoid interference with a patient""s surrounding soft tissue anatomy.
Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description of the drawings and the preferred embodiments.